Chevy Small Block Testing - Legendary Small-Block Shootout

Where else but in the pages of Super Chevy are you going to see a test of three legendary small-block Chevys? Under the Comp Cams valve covers sit a DZ302, an L76 327 and an LT-1 350.

If you have even an ounce of Bow Tie blood, you will immediately recognize the three names presented above as nothing less than legendary small-blocks. During the muscle car era of the '60s and early '70s, this trio carried the torch into battle for their respective displacements. Sure, the fuel-injected version of the 327 was rated 10 hp higher than the carbureted L76, but both shared the same internal components.

The DZ302 came about because of the need to produce a 5.0L displacement powerplant for the popular SCCA Trans-Am sedan racing series. The LT-1 350 represented the last hurrah for the high-squeeze, solid-lifter small-blocks, as the '71 version made due with just 9.0:1 compression compared to 11.0:1 for the 1970 model.

We all know now that the power ratings in the old days were somewhat suspect. The manufacturers played games with the official power ratings in order to appease the buying public, insurance companies and racing officials alike. Offering their engines with elevated ratings was not uncommon, as horsepower sold cars and with the lack of available dynos to verify the claims, it was difficult to tell the difference between a 350hp engine and one rated at 370hp.

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Before we could officially test these legends, we had to source three blocks. Our trio came from L&R Automotive in Sante Fe Springs, California.

Speaking of ratings, it is also important to note that these differed wildly from those used today by the OEMs. Where the new LS3 small-blocks are tested to the latest SAE net (flywheel) standards and are rated with full accessories, exhaust and the factory induction system (basically the way it comes in the car), pre-1972 engines were rated in optimized condition sans accessories (open dyno headers, no accessories, no air inlet restrictions, etc.). What this means is that a 370hp LT-1 from 1970 is actually much closer in actual power output to the 300hp LT1 circa 1995.

Regardless of the differences in the power ratings, what we really wanted to know was just how each of these legendary small-blocks compared to each other. Was the output of the high-winding 302 really closer to the often-touted 400hp than the rated 290 hp? Was the 365hp 327 more than a match for the later 370hp LT-1 350? After all, both the 302 and 327 shared slightly wilder cam timing than the LT-1, but would the milder cam timing offset the additional displacement? Would the shorter stroke small-blocks make more peak power than the long-stroke 350? These were all questions that deserved answers and these answers had to come from more than the recollection of some racer who ran one back in the day.

This is one of those times when a simple session of bench racing snowballs into a monster of a dyno project. Obviously, the only definitive answer had to come from the dyno. Real back-to-back testing was the only surefire way to provide not just peak power numbers for each, but overall power curves. After all, man does not live by peak power alone. It is the average power production that provides the key to a successful street powerplant, and since all three of these production small-blocks were indeed street motors, we needed to test them.

Testing three legendary engines meant building three legendary small-blocks. Luckily for us it was unnecessary to reproduce the motors down to the last casting number. Basically all we needed to do was pay close attention to the engine specs of each and duplicate these where necessary. There were a few mandatory items in each build up, namely things like 11.0:1 compression, the proper cam specs (duplicates of the original) and original big-valve "fuelie" cylinder heads. While each of the motors was adorned with different casting numbers, the reality is that the big-valve performance heads were much more alike than different.

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Where else but in the pages of Super Chevy are you going to see a test of three legendary small-block Chevys? Under the Comp Cams valve covers sit a DZ302, an L76 327 and an LT-1 350.

Before we could officially test these legends, we had to source three blocks. Our trio came from L&R Automotive in Sante Fe Springs, California.

Though two-bolt blocks would be more than sufficient for these production motors, we were fortunate enough to locate three four-bolt blocks for our testing.

L&R performed all the necessary machine work to the blocks, including boring them 0.030-over before covering them in a solid coat of Chevy orange.

Each of the four-bolt blocks received a dedicated crankshaft. L&R supplied both a small-journal 283 steel crank (original large-journal DZ steel cranks were well out of the budget) and matching large-journal 327 cast crank. Pro Comp supplied a new forged steel 350 crank. The cast 327 crank was deemed plenty strong for our dyno testing and ran to 7,000 rpm with no problems.

L&R gave the cranks a once over including polishing. Without its support this major project would be just another good idea.

Installation the small-journal cranks in the large journal blocks was made possible with the use of Clevite spacer bearings (PN MS1110H). Clevite also supplied the standard bearings for the large-journal 350 crank from Pro Comp.

The pistons and rods for our legendary trio came from a variety of sources. All three sets of pistons came from Probe Racing, while Pro Comp supplied the forged rods for the 327 and 350.

Crower came through with the small-journal rods for the 302. Due to the availability of pistons (specifically compression heights versus dome size), all three of the engines were run with 6.0-inch rods. While the factory motors all had 5.7-inch rods, this would have little to no effect on the power output.

Since all three small-blocks came from the factory with 11.0:1 compression, the different displacements required different piston domes. The 302 required 12.5cc domes, the 327 just 7.5cc and the 350 produced the requisite 11.0:1 compression with 2.5cc domes.

Naturally our new short-blocks required the proper head gear. Each small block received the requisite "fuelie" heads to ensure accurate data.

Even though the vast majority of so-called fuelie heads flow similar numbers, we actually went to the trouble of sourcing the proper casting numbers for each combination. The early 327 received 461 heads while the 302 and 350 received 186 and 492 castings, respectively.

Each of the heads featured the small 64cc combustion chambers. We measured all of the chambers and found them to be all within 1cc of each other (all were very close to 62cc).

The heads all received new 2.02/1.60 stainless steel valves, valve springs (with 125-130 pounds of seat pressure) and factory retainers. Each head was given a factory-style valve job but no porting of any kind was employed to the otherwise stock castings.

The flow rates for all of the heads are listed in the head flow data chart, but know that most big-valve performance (production) heads offer very similar flow numbers. There seems to be as much difference between two sets of heads of the same casting number as two set of different casting numbers.

All heads received rocker studs and guide plates from Comp Cams along with hardened pushrods (7.8-inches in length).

Comp Cams also supplied three sets of the factory long-slot rocker arms.

To ensure accurate data, all of the heads were flowed on the airflow bench. Testing revealed that what we thought was a set of as-cast 461 heads turned out to have ported exhaust ports (though cleverly disguised). Since we didn't have another set of 461 heads ready for testing, we ran the 327 with the 186 heads from the 302.

After flow testing, the heads were installed on the awaiting short block using the Pro Comp head gaskets and ARP head bolts.

If you are looking for an original carb for your legendary small-block, look no further than Pony carburetors. It supplied this 780 Holley (3310) for the DZ302, but rather than ruin this numbers-matching carb by disassembling it for the necessary jetting and secondary spring (required due to the use of headers and lack of accessories), we opted to run a modern Holley 750 HP carb.

After installation of the MSD distributor, we ran the DZ302 in anger. Originally rated at 290hp, the 302 produced peak numbers of 357hp and 332 lb-ft of torque. Though the power peak occurred at 6,600 rpm, the motor pulled strong all the way to 7,000 rpm (and still producing 352hp).

Next on the dyno was the L76 327. Rated at 365hp, the 11.0:1 327 actually produced 352hp. The larger displacement not only offered more torque (364 ft-lb vs 332 lb-ft for the 302), but reduced the respective power peak engine speeds compared to the smaller 302.

The final high-compression motor to be tested was the legendary LT-1. Rated at 370hp (360 in the Camaro), the LT-1 produced 353 hp and a whopping 392 lb-ft of torque. The milder cam profile combined with the increase in displacement dropped the engine speed where peak power occurred even further (compared to the 302 and 327). Compared to the 302, the peak torque dropped by 400 rpm while peak power occurred 1,200 rpm earlier. The LT-1 offered as much as 80 lb-ft of torque over the smaller 302 early in the rev range but out past 6,000 rpm, the smaller 302 carried the power curve to offer better power over both the 350 and the 327.

After installation of the large-chamber 487 heads, the now-'71 LT-1 was run on the dyno. The drop in compression took its toll on peak torque, as the 9.0:1 LT-1 produced 382 lb-ft, but the extra airflow offered by the 487 heads made itself known by allowing the smog motor to produce the highest peak power of any of our four test combinations. All hail the '71 LT-1 with 362hp.

As luck would have it, we also had a set of 1971 LT-1 heads (487 castings with 76cc chambers) at our disposal. Replacing the 62cc chamber heads on our high-compression 1970 LT-1 essentially produced a low-compression 1971 LT-1 motor. This shot illustrates the difference between the small chamber 492 heads and the large chamber 487 heads.

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